This proposal is to establish the Resource Facility for Population Kinetics (RFPK). The purpose of RFPK will be to promote the application of computer modeling in biomedical research focusing on compartmental population kinetics. Population kinetics in the methodology used to quantify inter-subject variability in kinetic studies. It is widely used in pharmacokinetic studies since it is the key to the understanding of how drugs behave in humans and animals. In metabolic (e.g. tracer) kinetic studies, it is used to identify those parameters in a model which change when comparing two populations. A growing number of researchers are recognizing the importance of software tools in this area and the need for individuals with the expertise to develop and apply them. RFPK will provide that expertise as part of fulfilling its goals which are: (1) the development and application of modeling technology to biomedical problems, 92) the development of general purpose algorithms for population kinetics, and making these algorithms easy to use through the development of graphical user interfaces for compartmental models, (3) supporting collaborative projects which help in the design and application of the software tools, (4) providing service and training to our user community, and (5) disseminating our technology, expertise and accomplishments. The proposed software tools will be designed in a modularized fashion. Some modules will be made available to other software developers thus extending the areas of application of the new computational capabilities. The software tools will be developed and released in stages so that users can start applying the technology and give feedback for future developments. What will make these tools unique is that there is no one software package that provide both easy model building capacity and the standard population kinetic methodologies: parametric, non-parametric, and two-stage. Thus the software tools will greatly enhance the overall quality of research in all types of kinetic studies. RFPK is distributed at two major universities both of whom contribute unique expertise to the project. The Administrative Core is located at the University of Washington.